The plan at a glance

This trellis stands on the north side of a 4 × 8 ft bed: a 2 × 4 upright against each north corner post, screwed to the post and through the wall, and a 2 × 4 rail across their tops. The rail is 6 feet above the soil, the height UW–Madison Extension gives for the tops of a vertical trellis’s posts, and the net between the uprights is about 6 ft 11 in wide and 5 ft 8½ in tall.

On the north side it shades nothing: University of Maryland Extension places taller crops on the north and west sides of a bed so they do not shade shorter ones. The sizes on this page are for the 4 × 8 cedar plan, 11 inches tall and filled 10 inches deep; any 4 × 8 bed with a post inside each corner takes it the same way.

From above, drawn to scale: the uprights stand against the two north corner posts, the rail runs between them, and the net hangs from the rail.

Boards, screws and netting

Use untreated wood: UW–Madison Extension says not to use chemically treated wood for stakes. Cedar matches the bed, and the Western Red Cedar Lumber Association recommends stainless steel screws for it (double hot-dipped galvanized will do). The counts below are for one trellis.

What to buy and cut for the trellis
Part	Size	Where it goes	Pieces
Uprights	2 × 4, cut to 82 in	against each north corner post, on the ground inside the bed	2
Rail	2 × 4, cut to 86 in	across the uprights’ tops	1
Screws	stainless steel, 3 in	3 through each upright into its post, 2 through the rail into each upright	10
Screws	stainless steel, 2½ in	2 through each wall board into each upright, from outside	8
Netting	nylon, about 4-inch squares	between the uprights, under the rail	about 7 × 6 ft

Build it

1. Stand a 6 ft 10 in upright in each north corner, its wide face on the corner post, and screw it to the post and through the wall.

2. Screw the 7 ft 2 in rail across the uprights’ tops, level, 6 ft above the soil.

3. Tie the net to the rail and uprights, about 6 ft 11 in wide and 5 ft 8½ in tall, and plant the climbers under it.

Build the bed first, or use your own 4 × 8 bed with a post inside each corner. Decide which long side faces north: the trellis goes there.
Cut two 2 × 4s to 82 inches for the uprights and the third to 86 inches for the rail.
Stand an upright in each north corner, on the ground inside the bed, its wide face against the corner post and its edge against the north wall. Hold it plumb with the level and drive three 3-inch screws through it into the post, then two 2½-inch screws through each wall board into its edge from outside.
Lay the rail across the uprights’ south edges, its top flush with theirs. Check it with the level and fix it with two 3-inch screws into each upright.
Tie the netting to the rail every few squares, then down both uprights, and let it reach the soil. Pull it taut so it does not sag under the vines.
Plant the climbing crops in a row along the north wall, under the net, and lower crops in front.

What to grow on it

UW–Madison Extension names pole beans and peas, tomatoes, cucumbers, gourds, melons and squashes among the vine crops that grow best on supports. Beans, peas and cucumbers climb a net on their own. Tomatoes do not form tendrils, so tie them to the net as they grow, and larger fruit such as melons may need a mesh bag or a nylon sock for support, the same page says. Illinois Extension adds that cucumbers grown up a support grow straighter.

With the climbers in the back row, the front 3 feet of the bed stays free for lettuce, carrots and other low crops: the planting layouts for a 4 × 8 bed show what fits.

At the end of the season

UW–Madison Extension suggests letting the vines dry on their support until they are brittle, so they break apart for easier removal. Taking the structure down for the winter is your choice, it adds; doing so spares it wear, especially a wooden one. Untie the net and leave the frame, or unscrew the rail as well.

What this plan does not cover

This is a plan for a trellis on a board bed on open ground. It is not an engineered structure and makes no load rating. A net full of vines catches the wind: in an exposed garden, untie the net when the crop is done. To cover the bed instead, the hoop cover calculator works out the hoops and the cover; for an arch between two beds, see the cattle-panel arch in the raised garden bed ideas.

Try it with your numbers

Put in your own bed and the raised bed soil calculator works out the answer as you type.

Open the raised bed soil calculator

References

Trellising, Staking and Caging – Vertical Gardening Techniques for Vine-Type Vegetables, University of Wisconsin–Madison Division of Extension.
Planning a Vegetable Garden, University of Maryland Extension.
Starting a Garden: Supporting Plants, University of Illinois Extension.
Fasteners for Outdoor Projects, Western Red Cedar Lumber Association.

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How to add a trellis to a 4 × 8 raised bed